Influence of Lung Hyperinflation on Respiratory Muscles Pressures During a Submaximal Test in Patients With COPD: A Clinical Perspective

Abstract

Background and Objective: Reduction of exercise tolerance is associated with expiratory flow-limitation (EFL) and lung hyperinflation; those are only partially reversible to bronchodilator. Lung hyperinflation lowers the diaphragm muscle provoking a mechanical disadvantage that, eventually, reduces maximal inspiratory (MIP) and expiratory (MEP) pressures. We aimed to assess the influence of the dynamic lung hyperinflation on respiratory pressures changes at rest and after a submaximal exercise test in COPD patients with and without a bronchodilator. Methods:: We prospectively analyzed 16 COPD patients (FEV1 36.4±10% pred.; age 61.0±8 years, height 165±12 cm and BMI 25.9±6 kg/m2). MIP and MEP were measured before and after performing the six minutes walking test (6MWT) with and without bronchodilator (400 mcg of albuterol). Results:: Nine of 16 patients increased IC more than 150 ml after bronchodilator use. Right after the 6MWT was accomplished without bronchodilator, IC decreased by 7.05% as compared to the 6MWT baseline value (p<0.01). Nine patients decreased IC more than 150ml. After bronchodilator use, patients performed the 6MWT without any IC significant reduction (p>0.05). Twelve patients increased the MIP (ranging from 70±11cmH2O to 77±10cmH2O, p = 0.0043) using 400mcg of albuterol. Thirteen patients reduced MIP after the 6MWT without bronchodilator use (p <0.007). There was no significant reduction (p> 0.05) in MIP when patients performed the 6MWT after bronchodilator use. We also found a significant correlation between MIP and inspiratory capacity (IC) and MEP and the IC before and after the 6MWT (r=0.61, p=0.0054; r=0.60, p=0.0031, respectively). Conclusions:: Dynamic pulmonary hyperinflation directly interferes with the ability of respiratory muscles to generate inspiratory and expiratory pressures. The previous use of bronchodilators in patients with COPD reduced dynamic hyperinflation when accomplishing a sub-maximal exercise.